Collimating optical sight with transparent mirror means



x, w f A- :l @f l J i; ff .f I/ z' Q [VCT: '5,4 May 1l, 1948. l T. D.MARTIN 2,441,160

COLLIMATING OPTICAL SIGHT WITH TRANSPARENT MIRROR MEANS Filed Feb. 9,1945 THOMAS D. MARTIN @M @Lum/Mw@ O,

www

Patented May 11, 1948 CLLEMATING GPTICAL SIGHT WITH TRANSFARENT MIRRRMEAN S Thomas D. Martin, United States Navy Application February 9,1945, Serial No. 576,998

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) 2 Claims.

This invention relates to improved optical gun sight particularlyadapted for use on aircraft havingr guns mounted in xed positions withrespect to the craft. One Well known sight consists of a sheet oftransparent material, such as glass, mounted in the craft in such aposition that the pilot can View the target through it. The target isvisible through the transparent sheet just as though the sheet were notthere. Because of the angle at which the transparent sheet is mounted,it catches and reiiects to the eye the image of the reticle which isinserted Within the sight. The optical system of this unit occupies muchspace which. is essential to the operation of the aircraft. This oldstructure also produces an image of lou.1 luminosity.

The object of this invention is to provide a sight unit of the typedescribed above which is compact and provides a clear image. Anotherobject is to provide an optical system which may include a plurality ofthese sight units cooperating to project a single apparent image on ascreen. A further object is to provide an optical gun sight utilizing alight source of reduced in tensity. Still another object is to provide asimple system for producing an image with a minimum vertical dimension.Other objects of the invention will appear from an examination of thedescription and drawings wherein:

Fig. 1 is a rear View of the device in section along line A-A of Fig. 2;

Fig. 2 is a plan view of the invention broken along line B-B of Fig. 1;and

Fig. 3 is s. View in section along line CC of Fig. 1,

Reference is had to the accompanying drawings Which illustrate twooptical units and whereinlike numerals refer to like part-s throughoutthe figures. The source of light l positioned in the light tight box 2is illustrated as a conventional incandescent lamp but any other sourceof high intensity may be employed. A plane mirror 3 or, as illustrated,a plurality of mirrors 3 disposed at an angle of 45 to the vertical arepositioned in the box adjacent the light source. I'hese mirrors are ofsuch size and shape as to t snugly in the box and shut out all lightfrom the light source l. A concave spherical mirror 4 or as illustratedin the drawing, a plurality of these mirrors are positioned in the box 2with their axes normal to the vertical plane and intersecting the planemirrors 3 which are perforated at the points of intersection of theseaxes to provide apertures v5. Plates 6 are mounted in apertures in plansnormal to the axes and with the center of the plate coincident with theaxes. Openings 'l formed in these plates in the configuration of thereticule of a conventional gun sight provide the source of the luminousoptical image and are positioned at the focal point of spherical mirror4. Lenses of the type known as Schmidt corrector plates 8 are mounted ina horizontal plane in the top of box 2 in the path of light reected fromthe concave spherical mirrors 4. These lenses correct the beam forspherical aberration and coma to provide clear cut edges to the imageand they further assist in collimating the beam. A transparent planereflector plate 9 is located on top of the box at a angle to thevertical and in the path of beams of light projected from the variousspherical mirrors and from which is reected the apparent optical imageil. This plate is positioned so that the gunner looks through it infiring.

The operation of the device is as follows: Light from the source l isprojected through reticule openings 'l in plates 6 against the sphericalmirror. 4. As the openings 'l are at the focal points of the sphericalmirrors the images are reproduced at infinity. The direction of eachbeam is changed through an angle of 90 by the' plane mirror 3 andprojected on the transparent refiector plate 9. The Schmidt correctorplates 8 interposed in the paths of the beams are ground to present aclear image. The reflector plate 9 is transparent, by reason of which alarge portion of the light from the reticule passes through it and islost. However, the portion of light reflected in the direction of theeye of the operator produces an image at infinity. As each beam producesits image at innity, the multi-ple images of the reticle will focus atinnity and will appear as a single image.

It will be understood that the above description and accompanyingdrawings comprehend only the general and preferred embodiment of theinvention and that various changes in construction, proportion andarrangement of the pa-rtsgmay be made within the scope of the appendedclaims without sacrificing any of the advantages of the invention.

The invention described herein may lbe manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

1. In a reflector gun sight a housing, a. plurality of perpendicularlydisposed concave mirrors at opposite ends off the housing with theirconcave surfaces facing each other, a plurality of plane mirrorsabutting each other at right angles and positioned between the concavemirrors and intersecting the focal points of the latter, each planemirror having a light transmitting opening at one of said lfocal points,a retlcle provided at each opening, luminaries behind the plane mirrorsto project an image of the reticles upon the concave mirrors, and atransparent plane -reectol upon which the images are reflected so as toappear at innity, said plane being disposed at an acute angle to thehousing.

2. A reflector gun sight comprising a housing, a plurality of planemirrors arranged at right angles to each other and at an angle of 45degrecs to the housing bottom and each having a light transmittingopening, ieticles at the opening in the plane mirrors, a plurality ofperedlcularlj: d corea" ri'rifers at the or posite ends oi' f surfaces-facing toward said plane mirrors, luminaries within the angle of theplane mirrors .to project images of the leticles to the concave l their.concave 4 mirrors, a means disposed in the path ol.' the reflectionsfrom the plane mirrors for correction of spherical aberration and coma,and a transparent plane reflector upon which the last reilectlons arereflected so as to appear at innity.

THOMAS D. MARTIN.

REFERENCES CTED rhe following references are of record ln the le of thispatent:

UNITED STATES PATENTS Number Name Date 1,958,035 Draper May 8, 19341,960,011 Ives May 22, 1934 2,170,979 Straubel Aug. 29, 1939 2,187,057Sauer Jan, 16, 1940 2,217,930 Zimmerman Oct. 15, 1940 2,295,779 ''-'u15, 1942 2,377,054 .f i ym-,y 19a? FOREIGN PATENTS Number Country Date437,44 Great Britain Oct. 28, 1935 624,129 Germany Jan. 13, 1933

